Campylobacter jejuni is a commensal bacterium of the gastrointestinal tracts of many animals, specifically birds. However, when C. jejuni infects the gastrointestinal tracts of humans, the bacterium often causes a mild to severe, bloody diarrheal syndrome. C. jejuni is currently recognized as a leading cause of food-borne bacterial gastroenteritis in humans world wide. The flagellum of C. jejuni has been identified as a virulence and colonization factor involved in promoting both pathogenesis and commensalism. However, knowledge regarding flagellar gene regulation and biosynthesis in C. jejuni is limited compared to other bacteria. We have found that C. jejuni tightly controls transcription of sigma 54-dependent flagellar genes encoding essential components of the flagellum. The overall objective of this proposal is to determine how the functions of key flagellar and regulatory proteins converge to control sigma 54-dependent transcription of flagellar genes. The central hypothesis of the proposed research is that C. jejuni coordinately requires FlhF, the flagellar export apparatus proteins, and the FlgS/FlgR two-component regulatory system for transcription of sigma 54-dependent genes essential for flagellar motility. The specific aims of this project are: 1) to assess the role of FlhF in flagellar gene regulation and biosynthesis; 2) to determine how flagellar assembly influences activation of transcription of sigma 54-dependent flagellar genes; and 3) to investigate possible additional layers of regulating flagellar gene transcription and biosynthesis and determine how these flagellar regulatory mechanisms may influence commensalism in birds. Accomplishment of these aims will aid in: 1) understanding connections between key flagellar proteins and how they influence genetic mechanisms to control flagellar gene regulation and biosynthesis; and 2) increase our understanding of genetic regulatory pathways used by C. jejuni for controlling expression of virulence and colonization factors. The bacterium Campylobacterjejuni produces a structure on its surface called a flagellum that is required for motility, promotion of diarrheal disease in humans, and colonization of animals. The proposed research activities will determine how certain proteins of C.jejunifunction together to control production of flagellar proteins that make up the flagellar structure.